Metallic, reflective material not displaying reflections of the World HDRi on EEVEE, how do I fix it?
I just checked out your .blend file. You don't need an irradiance volume or a reflection sphere to reflect the HDRI - in fact, in this case, it is messing with it. Irradiance volume only captures indirect light, and reflection sphere helps with SCENE reflections - but is not needed for WORLD reflections. It works if you delete them, and then delete the lighting cache - see below:

If you want to see more of the world reflected, I would also suggest you lower your roughness a bit, but that's up to you and what you want to use it for.
Cheers